as far as i have been told, and to date been practicing, all corals sft/lps/sps get the dip. i use the SeaChem iodine dip.
i do not dip other inverts (snails/shrimp/etc...), or obviously vertebrates.
-edit-
the list of things i have dipped so far includes:
scoly's
acans
favia
maze brain (platygryia)
chalices
motipora
sertiapora (bird's nest)
acropora
pulsing xenia
zoas
mushrooms
euphyllia (frogspawn/hammer)